The present disclosure relates generally to a radio frequency circuit device and method of controlling impedance, and more particularly to a low-power, low-cost radio frequency circuit device including a power amplifier and a low-noise amplifier coupled to an antenna without an intervening transmit/receive switch.
In many instances, radio frequency transceiver circuitry includes an low noise amplifier circuit for clear reception of a radio signal transmitted to the receiver and received through an antenna and includes a power amplifier circuit for transmitting a radio signal through the antenna to another device. Typically, power amplifier and low noise amplifier circuits are selectively coupled to the antenna through a transmit/receive (antenna) switch. Unfortunately, the cost of the antenna switch may be prohibitive for low-cost applications.
In radio frequency transceiver circuitry, impedance mismatches between transmission lines and circuit components will cause power losses due to signal reflections, resulting in degradation of transmission signal strength and signal-to-noise ratio. In an example, for desired performance and power, a power amplifier's output impedance can be matched to impedance associated with the transmission line extending from the power amplifier to the antenna. Similarly, for desired low-noise operation, the input impedance of low noise amplifier can be matched to impedance of transmission lines leading from the antenna to the low noise amplifier.
When the antenna switch is used to switch between transmit and receive modes, power amplifier and low noise amplifier can include their own impedance matching circuitry designed specifically for the transmit or receive modes. However, if the antenna switch were omitted, such mode-specific impedance matching would introduce impedance mismatches, degrading transmission power and decreasing the signal-to-noise ratio. Further, high peak voltages of the power amplifier in transmission mode could destroy a high performance low noise amplifier, which is typically not designed to handle such high voltage levels.
Accordingly, embodiments of a transceiver circuit are disclosed below that provide a new structure and technique for coupling a power amplifier and a differential input low noise amplifier to an antenna.